Myocardial infarction is the leading cause of death and disability in the United States today. While the treatment of acute myocardial infarction has received intensive study, there continues to be a paucity of scientific data regarding the fundamental causes of continuing disability and recurrence of acute episodes in these patients. Likewise, the causes for continuing disability in patients who have undergone coronary artery bypass graft surgery are not well defined. Therefore, we propose studies to examine the natural history of early recovery from myocardial infarction and coronary artery bypass graft (CABG) surgery, emphasizing the application of advanced biomedical technology to characterize the risk of recurrent myocardial infarction and sudden cardiac death, functional capacity, and psychological status within the first three months following hospitalization. The risk of recurrent myocardial infarction and sudden cardiac death is evaluated with respect to the incidence of exercise-induced ischemic ST depression, the incidence of spontaneous and exercise-induced premature ventricular contractions, and the plasma catecholamine concentration. The relationship between psychological status and risk of recurrent cardiac events is examined by correlating serial measurements of affective state and plasma catecholamine concentration. Changes in ventricular function are measured by echocardiogram during the stress of lower body negative pressure and supine exercise. The cardiovascular response to a variety of physical work loads encountered in occupational work is characterized in the laboratory. Recordings of heart, rate and blood pressure, made by portable devices, are utilized to evaluate the cardiovascular response to actual on-the-job working conditions. Treadmill exercise testing and individualized regimens of physical activity are applied during and soon after hospitalization in order to study their short-term effects on risk for recurrent events, functional capacity, and psychological status. The extent to which these short-term outcomes may be predictive of long-term outcomes may then be established by prospective study.